I. Field of the Invention
The present invention relates to a speed controller equipped with a device for protection against the overcurrents generated by the overvoltages or undervoltages on the electrical power-supply network.
II. Discussion of Background
In a known manner, a speed controller is connected to the electrical power-supply network and intended to control an electric load. It comprises a voltage rectifier module as input that converts an alternating voltage provided by the electrical network into a direct voltage and which feeds downstream a power bus equipped with a positive line and a negative line. A filter capacitor, commonly called the bus capacitor, is mounted between a positive terminal and a negative terminal of the power bus. As output the controller comprises an inverter module fed by the power bus, enabling generation, from the direct voltage, of an alternating voltage which may be of variable amplitude and frequency by using electronic switches, for example IGBT transistor switches controlled by Pulse Width Modulation (PWM).
The electrical power-supply network may undergo various types of disturbance such as overvoltages or undervoltages. The disturbances may be of high amplitude and short duration, hence weakly energizing, or of low amplitude and long duration, hence highly energizing. If the disturbances are highly energizing, some components of the controller such as the diodes of the rectifier module, the bus capacitor or the transistors of the inverter module may be damaged.